The investigation into the murder of British student Meredith Kercher in Italy took a dramatic twist yesterday when the family of one of the suspects was accused of attempting to interfere with the inquiry.

Police tapping the phones of the father of Italian student Raffaele Sollecito overheard discussions that appeared to suggest plans being made to get senior politicians to use their influence and get detectives whom the Sollecitos considered hostile taken off the case. The phone tap information is in files handed over to lawyers as magistrate Giuliano Mignini officially completed the investigation into the strangling and stabbing of Kercher, from Surrey, who was found on 2 November semi-naked in a pool of blood in her bedroom in Perugia.

'We've got to flay the Perugia flying squad,' a family member was overheard saying, according to the Italian newspaper Corriere della Sera. 'If we can get rid of the head of homicide and that other one, we'll be OK.'

Relatives of Sollecito, including his sister, a policewoman, were also overheard discussing politicians who could help their case. Giulia Buongiorno, a lawyer and MP in Silvio Berlusconi's ruling coalition, has now been retained to represent Sollecito. 'She can help out on this case at a political level,' Sollecito's father was overheard saying.

Sollecito's father, Franco, a well-to-do doctor from Bari in southern Italy, has campaigned to prove his son's innocence, even to the point of allegedly leaking to a TV station a video obtained from the crime scene showing Kercher's corpse, as well as highlighting perceived errors by the investigators, including the delayed recovery of parts of Kercher's bra strap which were found to carry Sollecito's DNA. Police are holding in custody Sollecito, 24; his former girlfriend and Kercher's flatmate, American student Amanda Knox, 20; and a third suspect, Rudy Guede, 21. All three deny involvement in the vicious killing.

The files also contain testimony of a witness who may prove vital for the prosecution. An Albanian, Hekuran Kokomani, told police he saw Knox and Sollecito outside Kercher's house on the night of the murder. The third suspect, Italo-Ivorian Guede, whom Kokomani knew, was also near the house, he said. As he approached, Kokomani was chased away by Sollecito and Knox, who had a large knife, he said. Kokomani first told police the encounter took place the night before the murder, but has now asserted it was the night that Kercher was killed. Knox and Sollecito claim they spent the night of the murder at Sollecito's house. Police have found a kitchen knife there that they believe could be the murder weapon, which has traces of Kercher's and Knox's DNA on it.

Kokomani also says he was offered €100,000 to return to Albania and not testify. A source in the investigation yesterday said police were not drawing conclusions about who offered the bribe and have yet to open an investigation into the alleged offer. Knox's mother has accused the police of bullying her daughter into confessing to the murder.